1. Field of the Invention
This invention relates to an image formation apparatus such as a copier or a printer and in particular to an image formation apparatus and an image forming method for superposing a usual image and an image formed using a special image formation material on each other for output.
2. Related Art
In recent years, attention has been focused on an art of using special paper with fine dots printed thereon (containing various sheet-like media) and inputting characters, an image, etc., handwritten on the paper by the user as electronic information (data). The input data is transferred to a personal computer, a mobile telephone, etc., and can be stored in a magnetic disk unit or any other storage or can be transmitted as electronic mail. In this art, small dots are printed on the special paper with a spacing of about 0.3 mm, for example, and the dots contained in a grid of a predetermined size draw a different pattern for each grid. The pattern can represent position information of an address, etc. Then, the pattern is read with a dedicated pen incorporating an optical read unit such as a digital camera, for example, whereby it is made possible to determine the position of the pen point and a move trace on the special paper. As information of the position of the pen point and the move trace is processed, it is made possible to use the handwritten characters and image on the paper as electronic information.
As this kind of related art, a large number of arts such as an art of printing a pattern on paper and an art of reading the pattern are proposed from various viewpoints. As the related art of forming a pattern on paper, for example, an art of providing a two-dimensional code pattern that can be printed with a document on demand using an existing office or home printer is available.
By the way, in the art of forming a code pattern representing the coordinates to determine a position on a plane on paper described above, generally an almost invisible colorant that cannot easily be identified by eyes of a human being is used to form a code pattern (for simplicity, the colorant to form the code pattern will be hereinafter referred to simply as “invisible” colorant). If a character, etc., is handwritten on paper where the code pattern is formed or if an image of an electronic document, etc., is superposed on the code pattern for print, the handwritten image or the image (which will be hereinafter collectively referred to as image) and the code pattern are visually recognized in a mixed manner and thus the invisible colorant is used to circumvent the difficulty of identifying the image.
The code pattern may be able to be read by a dedicated read unit as described above. Then, a code pattern is drawn using a colorant which allows a light beam in a visible light region to pass through and has a high absorption ratio of a light beam in any other region than the visible light (for example, near infrared region), and the read unit reads the code pattern using a light beam responsive to the nature of the colorant. Accordingly, it is made possible for the read unit to read while invisibility of the code pattern is ensured.
However, to form the code pattern using an invisible colorant as described above, it becomes difficult to determine whether or not the code pattern is formed simply by visual check on paper. Particularly, to print a code pattern using an image formation apparatus such as a printer, a situation in which the colorant (toner, etc.,) for the code pattern is insufficient and the code pattern cannot be printed although an image can be printed can occur. In such a case, if a human being sees printout paper, it is difficult for the human being to determine whether or not the code pattern is printed; this is a problem.